The primary effect of quinidine is on T waves and the QT interval. T waves become widened, flattened, and ultimately inverted. Marked lengthening of the QT interval can occur and can contribute to the proarrhythmic effect sometimes noted with quinidine. In addition, significant widening of the QRS occurs at toxic levels.
Figure 13.5 shows the precordial leads of a 75-year-old white female who had recently been started on quinidine for atrial fibrillation. This tracing
was taken just minutes after conversion from an episode of ventricular fibrillation precipitated by the proarrhythmic effect of quinidine. Note that the QT interval is prolonged and that the T waves are flattened and widened.
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